We have identified HNF3alpha , a member of the HNF3 forkhead family that bind to a consensus DNA sequence, as a new AR co-activator that is involved in androgen regulation and prostate-specific expression of the probasin (PB). HNF3alpha is expressed in the normal rodent prostate, our transgenic mouse models that develop preneoplastic lesions and in adenocarcinoma, and in all human prostate cancers examined. The closely related HNF3( forkhead protein was not expressed in the normal rodent prostate but was expressed in an androgen independent mouse neuroendocrine (NE) prostate cancer model and a subset of human prostate cancers. Expression of HNF3alpha in cell culture will increased androgen dependent AR activation of the PB and human Prostate Specific Antigen (PSA) promoters. Most importantly, co-expression of the HNF3beta gene with the PSA promoter-reporter in cell culture will activate the PSA promoter in an androgen-independent manner. Our Hypothesis is that HNF3alpha is key to normal prostate development and the expression of HNF3beta will switch androgen regulated genes to behave in an "androgen independent" manner. Our three Specific Aims are as follows: Aim 1: To characterize the HNF3 expression in the mouse UGS and prostate; Aim 2: To test the functional role of HNF3 proteins in prostate development; and Aim 3: To determine the role of HNF3alpha and HNF3beta in tumor development and progression. The overall goals of this grant are to establish the importance of the HNF3alpha in the normal development of the prostate and in androgen dependent tumor growth and the role of HNF3beta in rostate tumor progression to androgen-independence.